Liquid fabric conditioners are compositions that soften fabric. Such compositions are typically contacted with fabric in the rinse cycle of the wash process. Consumers desire an attractive appearance and excellent pourability of such liquids. Non-ionic ethoxylated surfactants with bulky ethoxylate (EO) groups help to make concentrated fabric conditioning compositions pourable. Non-ionic surfactants achieve this low viscosity by fragmenting the spherical liposome droplets into lamellar ‘sheets’ or disks of flat structure. Such non-spherical structures give the liquid a pearly lustre that is particularly liked by consumers. However, stability problems are known to persist with regard to the storage stability of compositions containing ethoxylate surfactants, particularly relating to optical and Theological aspects. The liquid thickens in the bottle and suffers loss of its pearly lustre. These problems are exacerbated at higher storage temperatures, such as are experienced in warmer climates or when ambient temperature rises. Thickening in the bottle leads to wasted product and, when used in automatic washing machines, messy residues being left in the dispenser draw of the machine. Ultimately this leads to a limited shelf life.
This high temperature stability issue arises from the collapse of the ethoxylate groups at elevated temperature and loss of steric repulsion that these groups afford the lamellar fragments as described in ‘Colloids and Surfaces A 288 (2006), 96-102, Colloidal stability of di-chain cationic and ethoxylated non-ionic surfactant mixtures used in fabric softeners’. The fragments adhere together and this size enlargement results in increase in viscosity of the composition and loss of the pearly lustre. At low ambient temperatures ethoxylate surfactants provide acceptable stability to the fragment structures.
Numerous publications disclose ways of improving the high temperature storage stability of liquid fabric softeners stabilised by ethoxylated non-ionic surfactants, for example, EP 523,922 and WO 01/46360.
The effect of ethoxylated nonionics with bulky headgroups on softener compositions is taught in WO 95/27769 where high levels of ethoxylated nonionics can be used to solubilise fabric softeners into micelles or micellar structures. These translucent liquids are claimed to be stable on storage and have good softening, dispensing and dispersing properties. Non-surfactant co-solubilisers such as urea, acid amides, citric acid, polycarboxylic acid, glycerol, sorbitol, sucrose and PEGs of MW˜200 to 6000 are mentioned.
WO 95/27771 teaches that amphoteric surfactants including betaines and tegobetaines can also solubilise fabric softeners into micellar structures to produce translucent liquids. Non-surfactant co-solubilisers are mentioned as in WO 95/27769. The compositions can be made either by co-melting of surfactant with softener and then adding to water or by sequential addition of components.
WO 93/23510 discloses the use of highly ethoxylated nonionic surfactants, cationic surfactants and their mixtures as viscosity/dispersibility modifiers for di-ester quaternary ammonium compounds to produce concentrated liquid compositions with improved-storage stability and viscosity characteristics. An optional liquid carrier can be included that is a mixture of water and low molecular weight solvents such as mono-, di-, tri- and poly-hydric alcohols. The composition is prepared by adding the melt of the softener to a solution of the single chain cationic surfactant.
As mentioned above the use of non-ionic surfactants as viscosity modifiers cause optical and rheological stability problems at elevated ambient temperatures.
We have now found that a combination of a single chain cationic surfactant, which is an amido-amine cationic quaternary ammonium surfactant, with a co-fragmenting agent, such as a polyol, in a concentrated liquid fabric softener composition containing an ester-linked cationic softener compound, unexpectedly gives rise to excellent storage stability of the concentrated fabric softener composition across a range of temperature conditions, including elevated temperatures. The liquid softener composition of the invention does not suffer from excessive thickening and the pearly appearance is preserved. This optical and Theological stability is achieved by compositions prepared using a specific order of mixing of the components, namely by adding a co-melt of the cationic softener and the single chain cationic surfactant into water containing the co-fragmenting agent.
Appearance of the Softener Compositions
Cationic fabric softener compositions form lamellar gel structures. This structure is characterised by stacks of alternate layers of cationic active and water. For electrolyte-free systems the thickness of the water layers could, in theory, be infinite. This means that small concentrations of cationic softener dispersed in water can give rise to a large viscosity or thick dispersion. When the concentration of cationic softener increases further the liquid becomes very thick and difficult to flow (i.e. it forms a gel). Therefore, aqueous liquid cationic fabric softeners with concentrations above ca 8 wt % require the use of a formulation aid.
To reduce the viscosity one needs to reduce the volume occupied by the large spherical cationic softener particles (called liposomes). One way to achieve this is by using micelle-forming surfactants to force the cationic softener to form smaller particles (or “fragments”), thus reducing the phase volume.
The appearance of the cationic fabric conditioner composition is related to its molecular arrangement. Desirable appearance is pearly or clear, whilst fabric conditioners which have a milky or marbled appearance are less luxurious and less desirable. These types of appearance are, for the purposes of this patent, as described below:
Milky: the liquid contains spherical liposome particles of cationic softener, which reflect light back at random giving it a whitish, opaque appearance.
Pearly: As the spherical liposomes are broken down into fragments, the liquid becomes less milky and more pearly. The fragments are tiny sheet-like flakes of liposome, which orient themselves to give a non-random reflection of light and a characteristic pearly appearance. This appearance is highly desirable for cueing a rich and luxurious liquid.
As mentioned earlier a problem with the desirable fragmented pearly liquids created by the use of ethoxylated non-ionics is that they are relatively unstable at elevated temperatures. Presence of perfume aggravates this instability and promotes faster thickening.
Clear: As the fragments get smaller and smaller, for example with addition of high levels of nonionic or cationic surfactant the liquid becomes more clear. High levels of solvent has also been used in the past to increase the clarity of these liquids.
Marbled: At elevated temperatures the fragments stick together and become large sheets resulting in the liquid appearance becoming striated with a marble effect. This optical change accompanies the thickening phenomenon where the flow property becomes stringy and undesirable. Such liquids do not disperse well in water.
It is an aim of the present invention to provide fabric conditioner compositions having a stable pearly appearance, which is maintained on storage under a range of temperature conditions.
We have now surprisingly found that the use of amido-amine single chain cationic surfactants in combination with a polyol such as sucrose or glycerol gives a synergistic improvement in stability. The pearly appearance remains unchanged.